This invention relates generally to a method for fabricating monolithic inkjet nozzles for an inkjet printhead, and more particularly to fabricating a refill channel for serving multiple rows of inkjet nozzles.
A thermal inkjet printhead is part of an inkjet pen. The inkjet pen typically includes a reservoir for storing ink, a casing and the inkjet printhead. The printhead includes a plurality of nozzles for ejecting ink. A nozzle operates by rapidly heating a small volume of ink in a nozzle chamber. The heating causes the ink to vaporize and be ejected through an orifice onto a print medium, such as a sheet of paper. Properly sequenced ejection of ink from number nozzles arranged in a pattern causes characters or other images to be printed on the paper as the printhead moves relative to the paper.
The inkjet printhead includes one or more refill channels for carrying ink from the reservoir into respective nozzle chambers. Conventionally a nozzle chamber is defined by a barrier layer applied to a substrate. The refill channels are formed in the substrate. Feed channels and nozzle chambers are formed in the barrier layer. A respective feed channel serves to carry ink from the refill channel to a corresponding nozzle chamber. A firing resistor is situated at the base of the nozzle chamber. When activated, the resistor serves to heat the ink within the nozzle chamber causing a vapor bubble to form and eject the ink. For thin film resistor printheads, resistors are built up by applying various passivation, insulation, resistive and conductive layers on a silicon die. The die and thin film layers form a substrate.
An orifice plate is attached to the substrate. Nozzle openings are formed in the orifice plate in alignment with the nozzle chambers and firing resistors. The geometry of the orifice openings affects the size, trajectory and speed of ink drop ejection. Orifice plates often are formed of nickel and fabricated by lithographic electroforming processes. A shortcoming of these orifice plates are a tendency to delaminate during use. Delamination begins with the formation of small gaps between the plate and the substrate, often caused by (i) differences in thermal coefficients of expansion, and (ii) chemically-aggressive inks. Another difficulty is in achieving an alignment between the firing resistors and the orifice plate openings.
Refill channels in the substrate conventionally are formed by sandblasting. A disadvantage of sandblasting is the time and expense to drill channels one at a time. Another shortcoming is that such method results in sand and debris in the facility--a potential source of contaminants.
A monolithic approach to forming inkjet nozzles is described in copending U.S. patent application Ser. No. 08/597,746 filed Feb. 7, 1996 for "Solid State Ink Jet Print Head and Method of Manufacture." The process includes photoimaging techniques similar to those used in semiconductor device manufacturing. An embodiment of the invention herein is directed to a method for forming a refill channel in the silicon die of a monolithic printhead. This is particularly significant for manufacturing pens according to existing geometries requirements. Existing inkjet pens have specific nozzle spacings and row alignments (i.e., geometries). Printer models for such pens include print controllers programmed to time inkjet nozzle firing patterns based upon such geometries. Proper timing is needed for proper placement and formation of characters and markings on a media sheet. Replacement pens for such inkjet printers often are required to conform to such geometry so that the timing implemented by the controller for the replacement pen still works for proper placement and formation of characters and markings on a media sheet.